The invention relates to a heat exchange cylinder that is devised for cooling or heating and drying of continuously extending materials, such as paper, fabrics, plastic foils, plywood and the like in the course of their further elaboration or production.
German Published Application DT-AS No. 1 134 272 made known a cylinder for cooling and drying longitudinally extending materials by means of heat exchange arrangements, which cylinder is formed as a double mantle hollow cylinder, having an annular space is provided with spiral streaming paths consisting of corresponding bridging sections whose heights correspond to the height of this annular space. Through said streaming paths, the heating or cooling medium streams in opposite directions from both ends of the cylinder. Because the streaming travel of the heat exchange medium is not straight, a relatively great flow resistance (due to the collision of the oppositely directed streams); results in a decrease in the streaming speed of the medium and in lessening of the heat exchange effect. Furthermore, the heat exchange medium is caused by the centrifugal force to create on the inner mantle surface of the outer cylinder a poorly heat conductive layer, the so called confine layer, since there are absent any technical means for swirling the same. This layer influences negatively the efficiency degree of the heat discharge from the travel way of the material into the heat exchange medium or in the reversed direction. The desired effect, namely that the heat passage value be kept dependent exclusively on the streaming speed of the medium, owing hereto is not achieved in the entire intended extent.
Besides, very often, as for instance in the case of cooling of printed paper, it proves to be disadvantageous that the oppositely directed dispatching of the heat exchange medium inside the cylinder creates different temperature zones on the cylinder surface.
In addition, the German Patent DT-PS No. 861.642 disclosed a double mantle drying cylinder for heating and cooling media which cylinder has an annular space with spiral-line streaming paths being formed by bridging sections that in their heights do not fully reach the inner surface of the outer cylinder mantle. Accordingly, the heating or cooling does not evenly occur by means of a medium streaming straightly in this cylinder. Quite sure, in comparison with the above mentioned cylinder, there exists here an only insignificantly lesser streaming resistance, because the height of the bridging section diverges from (unequal to) the height of the annular gap space in so far that a small portion of the medium over the bridging sections can touch the inner surface of the outer cylinder mantle. A weak whirling formation on the bridging sections causes only an insufficient portion of the medium confine layer (having a relatively poor heat exchange capacity and formed on the inner surface by the centrifugal force) is stripped off by the medium streaming speed. The high flow hampering resistance and the consequent relatively small streaming speed do not allow achievement of optimum heat exchange.
Owing to the low streaming speed of the involved heat exchange medium, the medium tends to adopt the temperature of the cylinder wall before is has traversed through the cylinder, i.e. it is already prematurely partially or totally saturated, so that along the cylinder axis no significant high temperature differences appear on the cylinder in the direction of the medium streaming, in other words, there can not be generated any too great temperature rise.
In order to achieve at least partially the desired cooling or heating effect, the known cylinders need a great quantity of the heat exchange medium. Where the question is of a medium for heating the cylinder, there accedes hereto a high energy consumption necessarily spent on its preparation.